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An enticing clue to a possible cause of colorectal cancer has been discovered by researchers at Dana–Farber Cancer Institute and the Broad Institute of MIT and Harvard. The research team, writing in the October 18, 2011, online issue of Genome Research, reports finding a strikingly large number of Fusobacterium cells in nine colorectal tumor samples. If the bacterium is implicated in colorectal cancer, it could be useful in diagnosing, preventing, and treating the disease.

A confirmed connection between Fusobacterium and the onset of colorectal cancer would mark the first time any microorganism has been found to play a role in this type of cancer, which is the second leading cause of cancer deaths in the United States.

The discovery was made by sequencing the DNA within nine samples of normal colon tissue and nine of colorectal cancer tissue, and validated by sequencing 95 paired DNA samples from normal colon tissue and cancerous colon tissue. Analysis of the data showed large amounts of Fusobacterium DNA in the tumor tissue.

Throughout the past decade, there has been an increasing focus on the relationship between cancer cells and their "microenvironments," specifically on the cell-to-cell interactions that may promote cancer formation and growth. While the relationship, if any, between colorectal cancer and Fusobacterium is unclear, there are intriguing hints that the bacterium may play a role in the cancer, says senior author Matthew Meyerson '89, an HMS professor of pathology and codirector of the Center for Cancer Genome Discovery at Dana–Farber.

"It may be that the bacterium is essential for cancer growth, or that cancer simply provides a hospitable environment for the bacterium," Meyerson observes. Researchers are now studying Fusobacterium levels in larger numbers of patients with colorectal cancer and in those without the disease.